The present invention relates to a semiconductor device and a manufacturing method therefor, and more particularly to structures of a gate electrode and a bit contact of a highly integrated DRAM and a manufacturing method therefor.
A conventional method of manufacturing a MOS transistor having a conventional metal gate electrode will now be described with reference to FIG. 1.
As shown in FIG. 1A, a gate insulation film 212 is formed on a P-type silicon semiconductor substrate 211, and then a polysilicon film 213, a barrier metal 214 for preventing reactions between polysilicon and a tungsten film and a tungsten film 215 are deposited. Then, a known lithography method and RIE (Reactive Ion Etching) method are employed to pattern gate electrodes. Then, gate electrodes are used as mask for ion implantation for implanting N-type impurities so that source/drain diffusion regions 216 are formed in the semiconductor substrate 211.
Then, a silicon nitride film 217 is deposited on the overall surface, as shown in FIG. 1B. Then, etching back is performed by the RIE method so that side wall spacers of the silicon nitride film 217 are formed on the side walls of the gate electrodes.
The above-mentioned conventional manufacturing method cannot form a contact hole of a type which approaches gate electrodes in a self alignment manner. That is, the contact hole can be formed when an insulation film 218 is formed on the overall surface, and then a contact hole 219 is formed in the insulation, film 218 by using a mask (not shown), as shown in FIG. 1C. What is worse, the tungsten film is exposed to a portion of the gate electrode after the gate electrodes have been formed (see FIG. 1B). As a result, there arises a problem in that the side walls of the gates cannot be oxidized and thus RIE damages or ion implantation damages cannot be restored. When the silicon nitride films 217 serving as the side wall spacers have been formed, the quality of the silicon nitride films deposited on the metal deteriorates as compared with the silicon nitride film deposited on the insulation film or polysilicon. Therefore, there arises a problem in that side walls having a satisfactory quality cannot be formed.